title: Characterization of a plasma membrane-associated plasminogen activator on thymocytes.
abstract: Plasma membranes isolated from normal thymocytes of hamster and rats were found to exhibit neutral protease activity toward 125I-labeled casein. The plasma membrane-associated proteases were completely inhibited by the serine protease inhibitors, diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride and p-nitrophenyl-p-guanidinobenzoate, partially inhibited by soybean trypsin inhibitor and antipain, but were only weakly inhibited by L-1-tosylamino-2-phenylethyl chloromethyl ketone. The plasma membrane-associated proteases were also completely inhibited by ZnCl2 (75--100 mu M), but they were not affected by several other divalent cations. The plasma membrane fraction contained a plasminogen activator activity which was specifically localized in this fraction. The plasma membrane-associated plasminogen activator activity was inhibited by all of the inhibitors which inhibited plasma membrane-associated proteases except L-1-tosylamido-2-phenylethyl chloromethyl ketone. Labeling of plasma membrane-associated serine esterases with [3H] diisopropyl fluorophosphate followed by separation of the proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that this fraction contained a single major 3H-labeled protein of Mr 105 000. Both the plasminogen activator and the Mr 105 000 esterase were shown to be glycoproteins by affinity chromatography on lentil lectin-Sepharose. These results indicate that the plasminogen activator of thymocytes is a glycosylated serine protease with an active site-containing subunit of Mr 105 000 which is specifically localized in the plasma membrane.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology*; D006224:Cricetinae; D005260:Female; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000378:metabolism; D010960:Plasminogen Activators / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D015849:Plasminogen Inactivators; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D013601:T-Lymphocytes / Q000201:enzymology*
chemical_list: D015849:Plasminogen Inactivators; D011480:Protease Inhibitors; D010447:Peptide Hydrolases; D010960:Plasminogen Activators